It seems to be a common problem that the plastic pipe that goes from the MAF to the Turbo expands due to heat/oil on the end that connects to the turbo, allowing unmetered air through the intake, I bet the majority of 2.5's are like this.
If this part is replaced it will before long expand again and allow unmetered air back in.
I had a look at mine today and it was very loose!, you could clearly see there was no seal as the crankcase breather is close to the end of the pipe and there was a trace of oil past the O ring on the turbo and at the end of the pipe, as it was heat that caused it to expand in the first place we will use heat to our advantage and fix it.
To repair this you will need the following parts:
1x 10mm & 7mm socket, ratchet & screwdriver that can accept sockets.
1x Molegrips or spring clip removal tool.
1x Glass jug (Not the other halfs best cooking gear!)
1x 50mm Juilblee clip.
1x New O ring from VW that sits on the turbo to seal the plastic pipe (I didn't use one as mine was fine, so will update post with a part number)
First remove the flexible pipe from the MAF to the plastic pipe by using a pair of molegrips to squeeze the spring clip or use a spring clip removal tool, I removed the pipe on the MAF and on the plastic pipe to gain more room.
Once that is out of the way remove the crankcase breather pipe from the top right of the plastic pipe and also remove the vacuum pipe behind it.
Have a feel of the plastic pipe and see if there is side to side/up and down movement, I bet it moves a fair bit!.
Going back to the front of the plastic pipe there is a 10mm bolt that holds the pipe and dipstick to the engine, remove this with a small 10mm socket, I used a bendy adaptor as it's a tight fit.
Once this is removed you can take the plastic pipe off the turbo, inspect rubber O ring and clean turbo/plastic pipe if needed.
Now go inside the house, fill your kettle up and set it to boil. While the kettle is boiling find a suitable container such as a glass bowl or jug, I used a pyrex measuring jug.
Put a 50mm jubilee clip on the end of the plastic pipe that connects to the turbo, make sure the 7mm bolt on the clip is facing the rear of the plastic pipe as per picture 1, nip it up slightly so it doesn't fall off but can't be moved if needed with a small bit of force
Once the kettle is boiled, fill the suitable container up with boiling hot water, never mind making a tea/coffee we don't have time just yet!.
Submerge the plastic pipe with the jubilee clip in the hot water and take this outside, be carefull!!, the hot water will allow the plastic to become soft, once it's been in there for a minute or two, take the pipe off and quickly put it on the turbo, ideally you need to get the bolt that secures the plastic pipe/dipstick to the engine in loosely to align it, if you can't get it in or don't have an assistant use a skinny screwdriver to locate the holes for now and leave it there till you are ready to bolt it up.
Once in place use a 7mm socket, extension bar and a screwdriver that takes sockets to tighten the jubilee clip, nip this up tight enough but do not overtighten it. The hot water allows the plastic to be plyable and the jubilee clip will shrink this down to the correct size, this should never expand with heat and work loose again!.
Connect the vacuum pipe up and then connect the crankcase breather hose back up.
Fit the pipe from the MAF to the Plastic pipe, put the metal clips back in the correct place.
Now you can make yourself a cuppa!